Computing systems use a printed circuit board which is referred to as a system board, logic board, or motherboard to connect all of the components of the system together. The board can include connectors for external components, such as power supplies, mass memory and user interface devices, slots for memory and add-on cards, and holes to connect pins of chips and discrete components such as capacitors, and resistors. These parts of the board are adapted to suit the particular computing system. The chips to be attached will also vary with different computing systems. In some cases, chips are soldered directly to the board and, in other cases, a socket is soldered to the board and then a chip is clamped into the socket. This makes it easier to replace the chip. The board provides a solid structure for attaching parts and also uses copper traces to electrically connect parts and connectors to each other.
In chip manufacture, the chips are being made smaller and more complex. In general, this reduces cost and improves performance. The reduced size results in less surface area for external connections and the increased complexity results in more external connections that will be made. The connections are made by solder balls or pins on the exterior surface of the chip. At the same time, the printed circuit board imposes a technical limitation on the density of the connections to the chip. There is a limit to how near two connections on a printed circuit board may be and still be physically and electrically separate from each other. This limit depends on how the printed circuit board is made. A less expensive printed circuit board will require more distance between nearby connections. In most cases, the chip is able to support much higher connection density than the printed circuit board.